The invention relates to pipe handling apparatus, and in particular to a clamp for holding and/or paying out under tension an elongate article, such as a steel or similar pipe line or cable in deep water, from the deck of a pipe laying vessel. The invention independently relates to a piston arrangement suitable for applying radial compressive forces on a pipe or other cylindrical member, for example in radial friction welding.
Various arrangements are known for pipe laying operations. For deep water applications, the xe2x80x9cJ-Layxe2x80x9d arrangement has been adopted, in which, a continuous steel pipe is launched into the water at a relatively steep angle, using a tiltable ramp or tower. Examples of such systems are known for example from U.S. Pat. No. 5,975,802 of the present applicant, and from WO-A-99/50582 and WO-A-99/35429. From these documents, it will be understood that a great weight of pipe has to be supported beneath the vessel to control the paying out of the pipeline. For this purpose, the known documents propose either track-type tensioners or travelling clamps to grip and control movement of the pipe. A number of methods are currently used to apply pressure to the friction surfaces of these clamps. To date these have been by direct pressure applied by screw jacks or hydraulic rams, levers, pressurised bladders, or cams. These solutions tend to be bulky and do not lend themselves to use on a J-lay ramp where the clamp must pass between work stations at each payout of the pipeline.
It is presently desired to work at ever-increasing sea depths, and each new project therefore demands greater and greater tensions to be handled by the apparatus on the ramp. In meeting this requirement, the ramp itself must become stronger and therefore heavier, and also the tensioner and/or clamp and lifting apparatus become heavier at the same time. Aside from weight and expense of the vessel becoming undesirably increased, this weight is located high above the waterline, and therefore creates stability problems in the design of the vessel as a whole. WO-A-98/48142 discloses a rack-and-pinion lifting arrangement as part of a drilling rig derrick. In this arrangement the weight of equipment to be lifted is taken by an articulated rack made of a large number of segments, running in a vertical main guide rail. The rack is incompressible longitudinally, and is driven from below by motors, such that the centre of gravity of the arrangement is not unduly raised. Moreover, the guide rails and tower themselves do not take the vertical load, and the derrick can therefore be of lighter construction itself.
Our co-pending application filed the same day and claiming priority from UK applications GB 0013569.9 (63566GB) and GB 0103861.1 (63591GB2) proposes using a travelling clamp for pipelay operations, which is carried by a rack-and-pinion lifting arrangement. While the present invention, relating to clamps and piston arrangements, will be illustrated in the context of such a system, the invention is not limited to trackbased lifting, or to travelling clamps in general.
The invention aims to provide an improved clamp for use in pipelay and other applications.
The invention in a first aspect provides a piston driving arrangement for use in pipe handling apparatus, including a piston member constrained to move along a first axis towards and away from a fixed support, wherein an hydraulically operated wedge member is driven transverse to the first axis so as to act between the piston member and said fixed support to effect said motion.
The wedge member may be keyed to said piston member so as to effect forcible movement of the piston in opposite directions along said first axis. In one example the keying comprises a dovetail channel and rail arrangement.
Further, the wedge member may be keyed to the fixed support, or otherwise constrained against movement of said support.
The wedge member of the piston driving arrangement may be connected to hydraulic means.
In one example a plurality of wedges are grouped by mechanical linkage to a common hydraulic actuator. The plurality of wedges in this example may be each driven individually.
Alternatively, the plurality of wedges may be grouped by hydraulic linkage to equalise actuating forces around the circumference of an object under pressure.
The piston arrangement may be part of a radial compression arrangement in which a plurality of such pistons have their first axes aligned radially. The piston driving arrangement of this type of configuration may be arranged so that it provides radial pressure in radial friction welding apparatus.
The piston driving arrangement may be part of a pipe clamp for use in pipe laying apparatus, for example, with the piston being the closing drive means of a pipe clamp for use in pipe laying apparatus.
The invention in a second aspect provides a clamp, for example, one adapted for use in pipe handling apparatus, the clamp including a plurality of ram arrangements mounted on a support and directed radially toward the centre of a workpiece object to be gripped, each ram arrangement comprising a push rod constrained to move in a radial direction and a wedge member driven in a direction across the radial direction and having an inclined surface so as to act between the push rod and said support to effect motion in said radial direction.
The wedge member in one embodiment is driven by hydraulic power. In a compact embodiment, the inclined surface is formed within the body of a hydraulic piston. Actuating surfaces may be provided at each end of said piston, the whole being mounted in a hydraulic cylinder, the push rod projecting through a side wall of said cylinder.
The inclined surface may be keyed to said push rod, so that the push rod can be pull as well as pushed along said first axis by the movement of the wedge member. The force therefore applied to the workpiece, such as the pipe, is a positively transmitted force and the ram is also positively withdrawn from contact with the elongate member when desired.
The keying of the push rod and the wedge may be by means of complementary angled keyways. The wedge member may similarly be keyed to the fixed support, or otherwise constrained against movement of said support.
A further clamp may be provided and controlled to operate in a set pattern. For example two co-operating clamps may be provided and operated so that the clamp may travel along the length of the elongate article and grip it in a xe2x80x9chand-to-handxe2x80x9d fashion.
The clamp may be openable to permit fitting around the article to be clamped.
The clamp may form a pipe clamp in a pipe laying apparatus, for example.
The clamp may alternatively be arranged to provide radial pressure in a radial friction welding apparatus of the type known from WO-A-97/32686, the contents of which are incorporated herein by reference.
The wedge member may be driven by hydraulic or pneumatic drive means. A plurality of wedge member s may be grouped by mechanical linkage to a common hydraulic actuator, or each may be driven individually. A plurality of wedges or groups thereof may be grouped by hydraulic linkage, to equalise actuating forces around the circumference of an object under pressure and being gripped.
The inclined surface of the wedge member may have an angle and surface configuration such that the driving force of the ram arrangement will be maintained in the event of power loss.
The push rod may have mounted at one end thereof a shoe which engages the surface of the workpiece to exert pressure thereon. The shoe may be shaped so that the surface engaging the elongate article engages the maximum surface area and the pressure is thereby more evenly distributed and points of excessive pressure are not formed. In one arrangement the shoe has an engaging surface which is part-cylindrical to mimic the outer surface of the elongate article.
The shoe may include a friction tile which is changeable. The configuration of the tile can be changed to suit the elongate article being laid (for example, its radius of curvature), and of course in the event of wear or damage.
The shoe may be connected to the push rod by means of a pivot joint such as a universal joint. This enables the shoe to pivot in one or two dimensions with respect to the axis of the push rod and thereby accommodate small irregularities of in the angle at which it engages the workpiece.
The shoes may be keyed directly to said support independently of the push rod so as to constrain movement under axial loading of the workpiece. This avoids the transfer of heavy loads to the ram arrangement and wedge member, for example, when clamping a heavy pipe during laying.
The invention in a third aspect provides a pipe handling apparatus wherein a travelling clamp is guided within an elongate structure, wherein said travelling clamp includes a ram constrained to move along a first axis towards and away from a fixed support, wherein a wedge is driven transverse to the first axis so as to act between the piston member and said fixed support to effect said motion. The further optional features of the invention in its first aspect may be applied, as set forth above.
Said elongate structure may be tiltable generally about a pivot point. Said pivot point substantially at deck level of a pipe laying vessel, the remainder of the structure being tiltable above deck level.
Drive means may be located within said elongate structure below said pivot point.
A rack may be provided for elevating and lowering said clamp under load with the arrangement being such that the load on the clamp when elevated acts in the rack, rather than directly on the elongate structure.
By these features, particularly in combination, the advantages of low weight and low centre of gravity can be brought to bear, while the clamp for pipe laying operations can itself be elevated for example 15 meters up and down the ramp or tower structure. Various ramp and tower arrangements known from the documents cited above and other sources can be adapted advantageously in this way.
When the drive means are carried in the structure below said pivot point, there is the advantage that the tension in the pipeline is transferred via the rack to the structure where it appears substantially as tension in the steel-work, rather than the compressive loads which are present in conventional travelling clamp structures.
Plural racks may be applied for balanced driving of the travelling clamp. Moreover, plural travelling clamps may be provided and driven by independent racks. The articulated rack below the drive means may reverse into secondary guide means parallel with the main guide means, or may be rolled or folded into a compact stowage space in the vicinity of the drive means.
The invention in a fourth aspect provides a ram unit comprising an hydraulic cylinder closed at both ends, an axial piston and a radial piston, the axial piston being arranged to slide within the cylinder between first and second hydraulic chambers defined by the ends of the piston and of the cylinder, the radial piston projecting through an opening in the side of the cylinder at a point always between the two ends of the axial piston, the axial piston and radial piston having complementary inclined surfaces, keyed to one another, so as to push and pull the radial piston in response to hydraulic pressure in the respective chambers.